Conventional round-rung extension ladders used by painters, carpenters and construction workers are frequently uncomfortable and may be dangerous to use because of the inadequate support provided by the round rungs of the ladder. Workmen using such ladders frequently stand on a single rung for a protracted length of time, causing fatigue and discomfort to their feet and legs due to the relatively narrow area of support provided by the rungs. Because the rungs have a rounded section they can also be hazardous because of little more than tangential contact with the sole of the user's shoes thereby providing minimal resistance to slippage.